1. Field of the Invention
The present invention relates to spring grip chucks and more particularly, to button releasing spindle chucks used in dental high speed handpieces for holding dental burs and drills.
2. Description of Related Art
There are currently known a wide variety of devices for insertion and removal of dental burs and drills in the head end of dental handpieces. These apparatus use push buttons or pressure piston, actuation levers, wedge shape plungers and other actuation means to disengage a clamping mechanism retaining a dental bur or drill in a dental handpiece to allow removal and insertion. The grip chuck spindles are retained in the rotational elements, bearings and impeller, of the head end of a dental handpiece.
U.S. Pat. No. 5,040,980 discloses a dental handpiece having a chuck with spring jaws that exert a griping force on a dental bur or drill. The jaws are opened to release the bur or drill by a lever at the upper end of the handpiece head. When the lever is moved upward, a wedge plunger is propelled between the jaws to spread them apart and release or insert a bur or drill. This and other lever actuated chucks have not been as widely used as the button actuated chuck spindles due to two major disadvantages. First, the movement of the lever is difficult and a tear in the doctors protective latex gloves is not uncommon. The second and larger problem is that the lever exerts double the pressure downward on the spindle chuck assembly which in turn is transmitted through the bearings supporting the spindle chuck resulting in premature bearing problems. Significant effort is being made to successfully convert these lever type chucks and caps to the preferred button actuating chucks and caps.
U.S. Pat. No. 4,874,314 discloses a dental handpiece having a socket which includes a sleeve that accepts a clamping sleeve which has two longitudinal slots extending inward to form resilient tongues which are moveable from a clamping position for engaging the bur or drill. The socket includes an axially movable ram which is actuated by a handle for the purpose of moving the tongues from the clamping position to an unclamped position to allow releasing of a tool. However the disadvantage of this design is in the ram and clamping sleeve where the ram has an outside tapered conical surface for engaging one end of the clamping sleeve which is provided with an inwardly tapered surface. To achieve the tapered conical surface on the ram, material thickness is minimal and is easily deformed when in use. If the ram tapered conical area is deformed during use the opening of the clamping sleeve does not occur and is unable to accept or release a tool. The other disadvantage is that the ram conical surfaces which are weaker than the clamping sleeve tongues, are to be used to spread the clamping sleeve tongues apart. If the ram tapered conical area flexes inward during use the bur or drill can not be accepted by the ram resulting in a failure to accurately position the bur or drill.
West German Patent No. DE 3402635 disclose a dental handpiece having a chuck with spring jaws that exert a griping force on a dental bur or drill. The jaws are shifted into bur/drill releasing or insertion position by depressing of a push button at the upper end of the handpiece head. When the button is depressed, a wedge plunger is propelled between the jaws to spread them apart and release or insert a bur/drill. However, field experiences with such a completed construction reveal operational problems that until the present invention have defied simple effective solution.
The present invention is structured to solve the currently available and disclosed devices assembly and operational problems for which there has been a long felt need in the dental industry. The grip chuck spindle assembly is designed for simple, easy assembly and for relatively smaller forces to install and remove burs and drills. The device is comprised of three parts, an outer spindle, a clamping bushing and a plunger, all of which are secured by crimping the bur end of the spindle against the clamping bushing bur end. The invention in the preferred embodiment is assembled by first inserting the plunger in the spindle followed by the clamping bushing with clamping fingers oriented toward the inserted plunger. The unit is operated by pushing the plunger to cause the wedge end to force the clamping fingers apart to allow insertion and removal of dental burs and drills. The simple operational approach and structure results in improved operational concentricity of rotational elements, reliability and less cost of manufacture.